<i>Introduction to Islamic Civilization</i>. R. M. Savory

We present the results of studying the spectral and photometric variability of the luminous blue variable star V 532 in M 33.The photometric variations are traced from 1960 to 2010, spectral variations from 1992 to 2009. The star has revealed an absolute maximum of visual brightness (1992)(1993)(1994), high/cold state) and an absolute minimum (2007-2008, low/hot state) with a brightness difference of ∆B ≈ 2.3 m . The temperature estimates in the absolute maximum and absolute minimum were found to be T ∼ 22000 K and T ∼ 42000 K, respectively. The variability of the spectrum of V 532 is fully consistent with the temperature variations in its photosphere, while both permitted and forbidden lines are formed in an extended stellar atmosphere. Broad components of the brightest lines were found, the broadening of these components is due to electron scattering in the wind parts closest to the photosphere. We measured the wind velocity as a difference between the emission and absorption peaks in the P Cyg type profiles. The wind velocity clearly depends on the size of the stellar photosphere or on the visual brightness, when brightness declines, the wind velocity increases. In the absolute minimum a kinematic profile of the V 532 atmosphere was detected. The wind velocity increases and its temperature declines with distance from the star. In the low/hot state, the spectral type of the star corresponds to WN8.5h, in the high/cold state to WN11. We studied the evolution of V 532 along with the evolution of AG Car and the massive WR binary HD 5980 in SMC. During their visual minima, all the three stars perfectly fit with the WNL star sequence by Crowther and Smith (1997).However, when visual brightness increases, all the three stars form a separate sequence. It is possible that this reflects a new property of LBV stars, namely, in the high/cold states they do not pertain to the bona fide WNL stars.

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“…We also use several estimations by Viotti et al [22], and one by Humphreys [29]. They are well consistent with our data.…”

Section: Photometric Observationssupporting

confidence: 91%

“…A more detailed description of all the photographic data is presented in [16]. We also use several estimations by Viotti et al [22], and one by Humphreys [29]. They are well consistent with our data.…”

Section: Photometric Observationssupporting

confidence: 83%

Spectral variability of LBV star V 532 (Romano’s star)

Sholukhova

Fabrika

Zharova³

et al. 2011

Astrophys. Bull.

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“…Star-forming regions in the Galaxy and in spirals are most often adjacent to dusty areas that mark molecular clouds (97), so a dearth of dark clouds in star-forming galaxies is unexpected. An exami nation of blue and red passband images, Balmer decrements, and optical and radio-determined star formation rates shows that even in and around star-forming sites, optical interstellar extinction in Irrs tends to be low [maximum E(B-V) � 0.5 (188,191,340) ; fo r the Magellanic Clouds, see, fo r example, 89,111,184,186,234,271]. This may be in part a reflection of the underabundance of heavy elements, which certainly results in some modifications of dust properties (e.g.…”

Section: Star-forming Complexes and The In Terstellar Mediummentioning

confidence: 99%

Structure and Evolution of Irregular Galaxies

Gallagher¹,

Hunter²

1984

Annu. Rev. Astron. Astrophys.

116

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INTRODUCTIONIrregular galaxies (Irrs) usually are smaller, less massive, and optically dimmer than commonly studied giant spirals, SOs, and classical ellipticals. At first giance they also appear to be rare objects that make up only a few percent of the major bright galaxy catalogs (87, 300). Is there then much reward in pursuing such faint and elusive galaxies? The answer to this question turns out to be a surprisingly strong "yes." An examination of more nearly complete samples of galaxies (213,341,366) reveals that Irrs account for it substantial (1/3-1/2) fraction of all galaxies, and that they certainly are dominant by number density among actively star-forming galaxies. A diversity of nearby examples therefore abound [including, of course, the Large and Small Magellanic Clouds (LMC and SMC)], making Irrs prime targets for detailed investigations of galactic stellar content and star fo rmation processes. Recognition of their structural simplicity has provided an additional stimulus for recent interest in Irrs as tests for theories of galaxy structure and evolution. These galaxies also are comparatively unevolved; and thus they may yield further rewards by allowing conditions to be defined in the poorly understood realm of low density extragalactic systems, which retain considerable information about galaxy formation (101, 327).In the broadest sense, the irregular galaxy class is loosely defined (e.g. see illustrations in 9, 23, 378,379). Hubble (175, 176) originally bu�lt on earlier nebular classification schemes (e.g. 153) and considered galaxies to be "irregular" if they showed chaotic, non symmetrical blue-light distributions, in contrast with the axial symmetry of normal "regular" systems. Later classification systems subdivide irregular galaxies into tWb major groups : Magellanic systems (Irr I, 1m), which resemble the Magellanic Clouds; and peculiar, often amorphous galaxies, which are classified as Irr II or 10 systems (72,174,290,292).Unfortunately, irregular structures may arise from a vari�ty of physical causes, and as a result a wide range of physical types of irregular galaxies are known to exist : (a) There may be substantial chaos in the projected stellar mass distributions in galaxies, although such nonequilibrium structures are unlikely to survive for more than a fe w rotation periods ("" 109 yr). Most currently kilOwn galaxies in disturbed states seem to be involved in galaxy galaxy intetactions (3 11, 358, 359, 384, 392, 393), although newly fo rmed galaxies could also find themselves in this situation (45). Some galaxies classified as Irr II or IO also belong in the category of interacting galaxies. (b) Similarly, unusual distributions of dense interstellar gas across the face of a galaxy may produce an optical image that is mottled by dark lanes. The dusty Irr II galaxies discussed by Krienke & Hodge (214) belong in this group. As these authors note, extended interstellar matter also can lead to emission filaments and reflection nebulae on galactic scales that give rise to abnormal optica...

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“…In Μ 31 and Μ 33, the radio emission from SNR is quite weak. As an example, an intense young galactic SNR such as Tycho (3C 10; 43 Jy at a distance of ~ 4 kpc) would have a flux density of only ~ 2 mJy at a distance of 600 kpc corresponding to the distance of Μ 33 (Humphreys 1980). A radio survey of Μ 31 SNR using the VLA has been carried out by Dickel et al (1982), who detected five SNR at 20 cm with flux densities in the range 1 to 3.4 mJy.…”

Section: Introductionmentioning

confidence: 99%